While glass mirrors have been common for centuries, they are not always appropriate for certain locations or situations, such as in public washrooms, gyms, locker rooms, etc., where the opportunity for vandalism and accidents or the possibility of liability from injury due to broken glass is increased. In these locations, builders have searched for other materials to be able to provide the washroom patrons with the amenities of a mirror, without the accompanying risk.
Additionally, such mirrors have found usage in optical systems such as large television sets, but they suffer from the same problems (i.e., breakage during shipment, handling or even manufacture).
For many years, polished metal plates have been used in this situation but with only partial success. While the plates are much sturdier and less likely to cause injury, the quality of the mirror is significantly decreased. The plates can become warped or dented, distorting the image. They also tend to have poor reflective characteristics thereby making the mirror image darker and harder to see. Mounting and/or replacing the plates can also become time-consuming and costly, since the plates are usually mounted to a wall by semi-permanent fasteners.
In any of these situations, glass mirrors can also have. their own drawbacks. First, they are generally quite heavy and break easily. Because the glass must be relatively thick to avoid being easily broken, the mirror image can be degraded, as the thick glass absorbs or diffuses some of the light passing through. Additionally, with the reflective material at the back of the glass for protection purposes, a dual image can occur from a slight reflection off the front surface of the glass, which then becomes a second reflective surface.
Glass is often molded and is therefore easily susceptible to imperfections in its thickness and planar surfaces. This results is warped and distorted images, such as those in carnival mirrors, although to a lesser extent.
To overcome these deficiencies, glassless mirrors have been developed that use thin reflective films as the reflective surfaces. U.S. Pat. No. 3,880,500 discloses a mirror having a thin reflective film stretched over a rectangular frame. The thin film consists of a plastic sheet with a vacuum deposited reflective layer of metal on one surface. To protect the layer of metal, the sheet is usually mounted with the metal layer facing inwardly. The plastic sheet acts as the reflective surface. The plastic sheet is thin enough to eliminate any double images due to a second reflective surface and is considered a first surface mirror. Some advantages of this type of mirror are that it is lightweight, economical, somewhat durable, and will not pose a hazard if broken.
In the mirror shown in U.S. Pat. No. 3,880,500, there are two films on opposite faces of the frame, secured to the frame edges through the use of contact cement or other adhesive. These two films and the frame enclose an inner volume of air that is in constant contact with the metal surface of the film. One drawback of this configuration is that the exposure to air and its constituents will likely lead to corrosion of the metal layer. If the layers are reversed, with the metal layer facing out of the mirror, it will be exposed not only to the air and its components, but to physical damage caused by incidental contact.